Thermo-Chemical and Mechanical Coupled Analysis of Swelling, Charring and Ablative Materials for Re-Entry Applications

Abstract

One of the major challenges in the design of atmospheric reentry vehicles is the optimization of the thermal protection system (TPS). During a reentry, the vehicle encounter severs heating and mechanical stress. A robust sizing is therefore essential to insure vehicle integrity and the mission success. In order to maximize the payload mass of the vehicle, lightweight charring ablators are commonly chosen as TPS materials for this one shot mission. To predict the behaviour of the TPS ablative materials under pyrolysis for reentry applications, Astrium ST initiated the development of a specific module of the finite element software SAMCEF: AMARYLLIS. This module uses the Finite Element Method to solve the problem of ablation and thermo-chemical degradation for 1D, arbitrary axis-symmetric or 3D meshes. The numerical model consists of three sets of equations, namely the heat balance equation, the mass balance equation and the charring equations. In order to enhance the current state of the art for the modelling of thermo-chemically decomposing materials through the integration of swelling behaviour, we used the SUPERVISOR module to elaborate a thermo-mechanical model of intumescing charring and ablative material. The SUPERVISOR is used as an interface-synchronisation module between MECANO and AMARYLLIS to realize a thermo-chemical and mechanical co-simulation. Current development of an ALE (Arbitrary Lagrangian Eulerian) method and thermal dependencies of the mechanical properties in MECANO allows taking into account various thermo-chemical reacting region and the ablating moving surface in the mechanically swelling behaviour. A global swelling model is built on the basis of various grounds testing such as plasma wind tunnel or IR furnace. The diversity of the experimental environment provided for the robustness of the swelling model. Through this thermo-chemical and mechanical coupling simulation optimal sizing of industrial case become possible.